The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Generally, an automatic transmission achieving more speed stages has been developed to improve fuel economy and drivability. Recently, increased oil price is triggering more competition in enhancing fuel efficiency of a vehicle.
Therefore, many researches for reducing weight and enhancing fuel economy in the auto industry through downsizing of an engine, and researches for securing drivability and fuel economy through multiple speed stages of automatic transmissions have been conducted.
However, in the automatic transmissions, the number of internal components (particularly, planetary gear sets etc.) increases so as to increase the number of speed stages, and as a result, a length of the transmission increases. Therefore, mountability, cost, weight, transmission efficiency, and the like are undermined.
In this aspect, in recent years, a hybrid transmission using motors has been used as the automatic transmission, and installability to the vehicle has been improved.
Particularly, a conventional 8-speed automatic transmission typically includes three to four planetary gear sets and five to seven engagement elements (frictional elements). In this case, since the length of the automatic transmission increases, installability may be deteriorated.